Convenienter inter virtutes morales ponuntur illae quae dicuntur principales, seu cardinales, quia perfectum est principalius imperfecto. Et ideo virtutes quae continent rectitudinem appetitus, dicuntur principales.
Those virtues which are called principal or cardinal are fittingly placed among the moral virtues because the perfect is principal as compared to the imperfect: and so those virtues which imply rectitude of the appetite are called principal virtues.
Huiusmodi autem sunt virtutes morales; et inter intellectuales, sola prudentia, quae etiam quodammodo moralis est, secundum materiam, ut ex supradictis patet.
Such are the moral virtues, and prudence alone, of the intellectual virtues, for it is also something of a moral virtue, as was clearly shown above (q57 a4).
Ambrosius dicit, super Lucam, exponens illud, "beati pauperes spiritu, scimus virtutes esse quatuor cardinales, scilicet temperantiam, iustitiam, prudentiam, fortitudinem". Hae autem sunt virtutes morales. Ergo virtutes morales sunt cardinales.
Ambrose in explaining the words, "Blessed are the poor in spirit" (Luke 6:20) says: "We know that there are four cardinal virtues, viz. temperance, justice, prudence, and fortitude." But these are moral virtues. Therefore the moral virtues are cardinal virtues.